Disk drive apparatus, head position control method, and hard disk drive

ABSTRACT

A position control system for a magnetic head improves servo tracking characteristics in a low frequency range without impairing the stability of seek operations. The position control system is equipped with two integrators: a first integrator  43  and second integrator  45.  The gain K3′ of the second integrator  45  is set larger than the gain K3 of the first integrator  43.  The first integrator  43  plays the role of offsetting the bias force acting on the magnetic head while the second integrator  45  plays the role of improving the servo tracking characteristics in the low frequency range.

[0001] This application claims the priority benefit of Japanese PatentApplication No. 2001-055997, filed on Feb. 28, 2001, and entitled “DiskDrive Apparatus, Hard Disk Drive, Filter and Method for Inspecting DiskDrive Apparatus.”

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates to a disk drive apparatus astypified by a hard disk drive and more particularly to position controlof a head that reads or writes data in a disk drive apparatus.

[0004] 2. Description of the Related Art

[0005] The hard disk drive is one of the most widely used externalstorage for computers. As is well known, the magnetic disk, which is astorage medium of the hard disk drive, uses a sector as the smallestunit of data recording: a disk surface is divided concentrically intotracks, which are further divided radially into sectors. The nearer tothe circumference of the magnetic disk, the higher the track recordingdensity can be made. Therefore, zone bit recording (Zoned BitRecording), which is the mainstream data recording method for magneticdisks, groups all the tracks into a number of zones and keeps the trackrecording density within each zone constant. Since a sector is normally512 bytes long, the nearer to the circumference of the magnetic disk,the more sectors the track contains.

[0006] The hard disk drive has a magnetic head for reading or writingdata from/to the magnetic disk. The magnetic head is mounted on anactuator mechanism which swings by means of a VCM (Voice Coil Motor).When the magnetic head reads or writes data, the actuator mechanismoperates to move the magnetic head to a designated track and position itthere. The process of moving and positioning the magnetic head is knownas a seek. The magnetic head seeks to a designated track based on servoinformation stored on the magnetic disk.

[0007] As described above, the tracks on the magnetic disk are dividedinto a number of sectors. Each sector constitutes a data area where datais stored. Besides, the magnetic disk contains servo areas where servoinformation is stored. The servo areas store track identificationinformation and burst patterns as the servo information. The trackidentification information represents the addresses of individual datatracks. It is read by the magnetic head to determine the track where themagnetic head is currently located. The burst patterns consists of anarray of multiple signal storage areas out-of-phase to each other. Theareas, each of which stores signals are laid at regular intervals in theradial direction of the magnetic disk. The signals output from the burstpatterns makes it possible to determine the amount of deviation of themagnetic head from data tracks. When data is read from or written to themagnetic disk, which is rotating, position control is performed bychecking the position of the magnetic head based on the servoinformation and driving the actuator mechanism and thus the magnetichead so as to correct any deviation.

[0008] 3. Problems to be Solved by the Invention

[0009] When a magnetic head reads or writes data to/from a designatedtrack on a magnetic disk, the positioning accuracy of the magnetic headcomes into question. With recent improvement in the recording density ofmagnetic disks, there is demand for high positioning accuracy. Thefactors that impair the positioning accuracy of magnetic heads includedisturbances. It is pointed out that disturbances can be caused by thetare weight of the actuator mechanism itself, the elastic force offlexible cables attached to the actuator mechanism, etc. In view ofthis, various techniques for positioning magnetic heads accurately havebeen proposed.

[0010] Data is read or written only after it is verified that themagnetic head is positioned accurately on a designated track. Therefore,even if a data read or write command is given, a data read or write mustwait until the magnetic head is positioned. The positioning controltechniques proposed so far have reduced the wait time for datareads/writes. However, it is reported that improved recording densityhas made it impossible to avoid the wait time for data read/writeoperations even with the positioning control techniques proposed so far.

[0011] Thus, it is an object of the present invention to provide atechnique that can reduce the wait time for data read/write operationseven on high density magnetic disks.

SUMMARY OF THE INVENTION

[0012] The inventor supposed that there may be some unreported factorswhich increases the wait time for data read/write operations, i.e.,lowers the positioning accuracy of magnetic heads. Thus, the inventorobserved the wait states for data read/write operations by operatingpersonal computers (hereinafter abbreviated to PC) equipped with a harddisk drive in various environments. As a result, it was found that therewere unreported factors which cause disturbances.

[0013] One of the factors is a CD-ROM drive fitted in the PC. That is,it was confirmed that low-frequency vibrations resulting from therotation of a CD-ROM during the operation of the CD-ROM drive causeddisturbances to the hard disk drive and that the servo's failure toabsorb the disturbances sometimes prevented data write operations to themagnetic disk. As a more specific example, a phenomenon was observed inwhich an application stored in a CD-ROM could not be installed on amagnetic disk. It had often been the case for some time thatapplications stored in a CD-ROM were installed on a magnetic disk.However, as there had been no report of installation failures, it can beinterpreted that further improvement in recording density caused theoperation of the CD-ROM drive to hinder the positioning control of themagnetic disk. Although the discussion here is concerned with a CD-ROMdrive, other devices that produce low-frequency mechanical vibrationsmay also hinder the positioning control of magnetic disks. Incidentally,the low frequency here means the frequency range not higher than 300 Hz.

[0014] Another factor is a portable telephone. There were cases in whichdata read/write operations from/to a magnetic disk were not carried outwhen a portable telephone was used around the PC. Further investigationconfirmed that low-frequency electrical noise produced by an operatingportable telephone entered the control system of an actuator mechanism,disabling servo tracking.

[0015] In hard disk drives, feedback position control including anintegrator is used for the position control of the magnetic head. Theintegrator is intended to detect the bias force acting on the magnetichead when the magnetic head is staying at a designated location on themagnetic disk and then offset the bias force by passing a currentequivalent to it through the VCM coil when the head seeks to thislocation the next time. Therefore, its gain cannot be increased.Consequently, when disturbed by low-frequency vibration and noise, itbecomes difficult to ensure servo tracking. Although it is expected thatservo tracking can be improved by increasing the integrator gain, thenthe integrator will not perform its intended function.

[0016] Servo tracking is required only during track following when themagnetic head is staying on a designated track, i.e., when data is beingread or written. Therefore, integrator gain is increased during thisperiod. Conversely, during seeks when the magnetic head is moving to adesignated track, the gain can be reduced, giving priority to offsettingthe bias force.

[0017] To implement this approach, at least two concrete measures areavailable: one of them involves using two integrators that generategains different in magnitude and operating them selectively as required,and the other involves using one integrator and switching its gains asrequired.

[0018] In view of the above, the present invention provides a disk driveapparatus comprising a disk-like medium for storing data; a head forreading or writing data from/to the above described disk-like medium; anactuator for moving the above described head to a designated location onthe above described disk-like medium; and position control means whichpositions the above described head by controlling the operation of theabove described actuator and which comprises a first integrator forgenerating a first gain and a second integrator for generating a secondgain larger than the above described first gain.

[0019] Since the disk drive apparatus of the present invention comprisestwo integrators, i.e., the first integrator for generating a first gainand the second integrator for generating a second gain larger than theabove described first gain, a gain can be selected according to theoperational status of the head. This makes it possible to offset biasforce during head seeks and ensure servo tracking during track followingagainst disturbances in the low frequency range.

[0020] To allow the selection of an integrator according to theoperational status of the head, it is desirable that the above describedfirst integrator and the above described second integrator be connectedin parallel. Then, when the above described head performs a seekoperation for moving to a designated location on the above describeddisk-like medium and a follow operation for reading or writing datastaying at the location, the above described first integrator can beoperated during the above described seek operation and the abovedescribed second integrator can be operated during the above describedfollow operation. More specifically, switching means can be providedbetween the above described first integrator and the above describedsecond integrator so that the above described first integrator willoperate when the above described switching means closes during the abovedescribed seek operation and that the above described second integratorwill operate when the above described switching means opens during theabove described follow operation. Incidentally, it is also possible toset the first integrator to operate simultaneously with the secondintegrator.

[0021] The present invention also provides a disk drive apparatuscomprising a disk-like medium for storing data; a head which performs aseek operation for moving to a designated location on the abovedescribed disk-like medium and a follow operation for reading or writingdata staying at the above described designated location; an actuator formoving the above described head to the above described designatedlocation on the above described disk-like medium; and position controlmeans which positions the above described head by controlling theoperation of the above described actuator and which comprises anintegrator for generating a corresponding first gain during the abovedescribed seek operation and generating a second gain different from theabove described first gain during the above described follow operation.

[0022] The disk drive apparatus of the present invention comprises anintegrator for generating a corresponding first gain during the abovedescribed seek operation and generating a second gain different from theabove described first gain during the above described follow operation.Therefore, by selecting between the first and second gains according tothe operation of the head, it is possible to offset bias force duringhead seeks and ensure servo tracking during track following againstdisturbances in the low frequency range. More specifically, the abovedescribed second gain can be set larger than the above described firstgain.

[0023] In the disk drive apparatus of the present invention, the abovedescribed integrator may consist of two integrators, namely, a firstintegrator for generating the above described first gain and a secondintegrator for generating the above described second gain.

[0024] In the disk drive apparatus of the present invention, the abovedescribed integrator may also consist of a single integrator. In thatcase, the above described integrator can be designed such that its gainwill switch from the first gain to the second gain when a change fromthe above described seek operation to the above described followoperation takes place.

[0025] The present invention provides a head position control method fora disk drive apparatus. That is, the head position control method of thepresent invention, which involves controlling the position of a dataread/write head on a storage medium based on servo information, controlsthe position of the above described head based on a first gain when theabove described head is moving over the above described storage mediumand controls the position of the above described head based on a secondgain larger than the above described first gain when the above describedhead stays at a designated location on the above described storagemedium.

[0026] In the head position control method of the present invention, theabove described first gain can be set to such a value that will ensurethe stability of operation while the above described head moves over theabove described storage medium until it stops at the above describeddesignated location. Also, the above described second gain can be set tosuch a value that will ensure servo tracking against disturbances in alow frequency range, specifically, in the frequency range not higherthan 300 Hz while the above described head stays at the above describeddesignated location.

[0027] A typical application of the present invention is a hard diskdrive. A hard disk drive according to the present invention comprises amagnetic disk on which servo information is stored; a magnetic headwhich seeks the above described magnetic disk and reads or writes datastaying at a designated location; an actuator for moving the abovedescribed magnetic head to the above described designated location onthe above described magnetic disk; and head position control means whichcontrols the position of the above described magnetic head based on theabove described servo information read out by the above describedmagnetic head and which comprises an integrator, wherein the abovedescribed integrator generates a first gain and a second gain largerthan the above described first gain, the above described first gainbeing generated when the above described magnetic head does not read orwrite data and the above described second gain being generated when theabove described magnetic head reads or writes data.

[0028] In the hard disk drive of the present invention, the abovedescribed first gain can be generated when the above described magnetichead is seeking. Also, in the hard disk drive of the present invention,the above described integrator may consist of a first integrator forgenerating the above described first gain and a second integrator forgenerating the above described second gain. Furthermore, the abovedescribed integrator may generate the first gain and second gain,switching between them.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a plan view showing the configuration of an HDDaccording to a first embodiment;

[0030]FIG. 2 is a diagram showing data storage areas and servo areas ona magnetic disk according to the first embodiment;

[0031]FIG. 3 is a block diagram showing the configuration for headposition control according to the first embodiment;

[0032]FIG. 4 is a block diagram showing the configuration of an MPU forhead position control according to the first embodiment;

[0033]FIG. 5 is a block diagram showing the configuration of a maincontrol section of the MPU for head position control according to thefirst embodiment;

[0034]FIG. 6 is graphs showing the frequency characteristics ofintegrators according to the first embodiment;

[0035]FIG. 7 is graphs showing the effect of differentiators accordingto the first embodiment;

[0036]FIG. 8 is a graph showing the effect of servo stability accordingto the first embodiment; and

[0037]FIG. 9 is a block diagram showing the configuration of an MPU forhead position control according to a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0038] The preferred embodiment of the present invention will bedescribed below with reference to the drawings. A hard disk driveaccording to a first embodiment of the present invention is disclosedbelow with reference to FIG. 1. As shown in FIG. 1, a hard disk drive(HDD) 1, which is a disk drive apparatus, has a disk enclosure 10comprising a box-shaped base 2 made, for example, of an aluminum alloyand a top cover 3 for sealing an open top of the base. The top cover 3made, for example, of brass is screwed to the base, interposed withrectangular sealing material (not shown). Therefore, the disk enclosure10 is airtight. FIG. 1 is a view in which part of the top cover 3 hasbeen cut away.

[0039] Inside the disk enclosure 10 is a spindle motor (not shown)consisting of a three-phase DC servomotor of a hub-in structure. Thisspindle motor rotationally drives a magnetic disk 4, which is a storagemedium. One or more magnetic disks 4 are installed depending on thestorage capacity required by the HDD 1.

[0040] Also, an actuator arm 5 is installed in the disk enclosure 10. Ithas its middle portion rotatably supported on the base 2 via a pivotshaft 7. A magnetic head 8 is mounted on one end of the actuator arm 5and a VCM (voice coil motor) coil 6 is mounted on the other end. The VCMcoil 6 and a VCM stator 9 consisting of a permanent magnet constitute aVCM 11. When current is supplied to the VCM coil 6, the actuator arm 5rotates toward a designated location on the magnetic disk 4. By means ofthis rotation, the magnetic head 8 performs a seek.

[0041] The magnetic disk 4 rotates around the spindle shaft of thespindle motor when the HDD 1 is in operation, but halts (stands still)when the HDD 1 is not in operation. As shown schematically in FIG. 2, aplurality of position information (servo information) storage areas 60are formed radially on the surface of the magnetic disk 4, and datastorage areas 61 are formed on the rest of the disk surface. The servoinformation, when read by the magnetic head 8, allows the location ofthe magnetic head 8 to be determined. It consists of trackidentification information and burst patterns. The track identificationinformation represents the addresses of individual data tracks. It isread by the magnetic head 8 to determine the track where the magnetichead 8 is currently located. The burst patterns consist of an array ofmultiple signal storage areas out-of-phase to each other. The areas,each of which stores signals, are laid at regular intervals in theradial direction of the magnetic disk 4. The signals output from theburst patterns make it possible to determine the amount of deviation ofthe magnetic head 8 from data tracks.

[0042] The magnetic head 8 is driven by a circuit such as the one shownin FIG. 3. The signal output of the magnetic head 8 is connected to aninput terminal of an amplifier (AMP) 21. The signals output from a leadelement of the magnetic head 8 are amplified by the amplifier (AMP) 21.The amplifier (AMP) 21 output is input in a microprocessing unit (MPU)23 via an analog/digital converter (A/D converter) 22.

[0043] The MPU 23 determines the position of the magnetic head 8, basedon the signals received from the A/D converter 22, and sends out signalsfor position control of the magnetic head 8 to a VCM driver 24, based onthe deviation between the determined position and target position of themagnetic head 8. In response to the input signals, the VCM driver 24outputs a drive current to the VCM coil 6 which composes the VCM 11.

[0044]FIG. 4 is a block diagram illustrating the functions ofmagnetic-head 8 positioning means implemented by the MPU 23. The signalsoutput from the A/D converter 22 are input in a current-head-positioncalculation section 31 and a burst pattern detection section 34. Basedon the inputted signals, the burst pattern detection section 34 checkswhether the magnetic head 8 matches the burst pattern storage area, andoutputs the result to the current-head-position calculation section 31.If the burst pattern detection section 34 determines that the magnetichead 8 matches the burst pattern storage area, the current-head-positioncalculation section 31 takes in the signals output from the A/Dconverter 22, calculates the current position of the magnetic head 8 inthe radial direction of the magnetic disk 4, and outputs the result.Therefore, the current-head-position calculation section 31 outputs thecurrent position of the magnetic head 8 at designated intervals. Thesefunctions may be implemented not only by hardware, but also by software.

[0045] A target head position setting section 35 sets and outputs thetarget position of the magnetic head 8 in terms of radial position onthe magnetic disk 4. The current position of the magnetic head 8outputted from the current-head-position calculation section 31 and thetarget head position outputted from the target head position settingsection 35 are input in a current-head-position signal generator 32,which then compares the position signals and outputs a signal y(n) whichrepresents the magnitude and direction of the deviation. The signal y(n)is input in a main control section 33, which sends out control signalsto the VCM driver 24 based on the signal y(n).

[0046]FIG. 5 is a block diagram showing the main control section 33 ofthe MPU 23. As shown in FIG. 5, the main control section 33 consists ofa proportional controller (gain K1) 41, first differentiator (gain K2)42, first integrator (gain K3) 43, second differentiator (gain K2′) 44,second integrator (gain K3′) 45, first switch 46, second switch 47, andfilter 48. Also as shown in FIG. 5, the proportional controller 41 isconnected in parallel with the first differentiator 42 and firstintegrator 43 while the first integrator 43 is connected in parallelwith the second differentiator 44 and second integrator 45. Theproportional controller 41 performs negative feedback control.

[0047] The first integrator 43 and second integrator 45 performdifferent functions. The first integrator 43 is intended to detect thebias force acting on the magnetic head 8 when the magnetic head 8 isstaying at a designated location on the magnetic disk 4, and then offsetthe bias force by passing a current equivalent to it through the VCMcoil 6 when the magnetic head 8 seeks to this location the next time. Byoffsetting the bias force, it is possible to speed up the seek to thedesignated location. For this reason, the gain of the first integrator43 cannot be increased too much. Consequently, the first integrator 43alone cannot ensure servo tracking against low-frequency vibrationcaused by the operation of a CD-ROM drive or against low-frequency noisecaused by the use of portable telephones. Therefore, this embodimentuses the second integrator 45. Since the second integrator 45 does notneed to offset the bias force acting on the magnetic head 8, its gain ismade larger than that of the first integrator 43. Specifically, if K3denotes the gain of the first integrator 43 and K3′ denotes the gain ofthe second integrator 45, K3 and K3′ are set such that K3<K3′. It isimportant, of course, that the gain K3′ of the first integrator 43 beset so as to improve servo tracking in the low frequency range againstthe low-frequency vibration caused by the operation of the CD-ROM driveand low-frequency noise caused by the use of portable telephones.

[0048] As described above, the first integrator 43 and second integrator45 have different purposes and thus should function at different times.The first integrator 43 should function during the seek operations ofthe magnetic head 8. However, if the second integrator 45 functionsduring the seek operations of the magnetic head 8, it will make the seekoperations unstable. Therefore, it is desirable that the secondintegrator 45 should function during track following when the magnetichead 8 stays at a designated location on the magnetic disk 4. Thus, thefirst switch 46 and second switch 47 are provided as the switching meansfor activating the second integrator 45 in addition to the firstintegrator 43. The first switch 46 and second switch 47 are opened andclosed in sync with the seek operation of the magnetic head 8.Specifically, during the seek operations of the magnetic head 8, thefirst switch 46 and second switch 47 are closed to activate only thefirst integrator 43. On the other hand, during the track-followoperations of the magnetic head 8, i.e., when data is read or written,the first switch 46 and second switch 47 are opened to activate thesecond integrator 45 as well. Although this configuration also activatesthe first integrator 43 at this time, it is also possible to adopt acircuit configuration that will activate only the second integrator 45.

[0049]FIG. 6 shows the respective frequency characteristics of the firstintegrator 43 and second integrator 45 as well as the frequencycharacteristics of the combination of the first integrator 43 and secondintegrator 45. As shown in the figure, the gain of the second integrator45 is set larger than that of the first integrator 43.

[0050] The use of only the first integrator 43 and second integrator 45would cause the phase to rotate, making the control system unstable.Thus, the first differentiator 42 and second differentiator 44 are usedin addition, as shown in FIG. 5, to correct the phase lag between thefirst integrator 43 and second integrator 45. FIG. 7 shows the frequencycharacteristics obtained by the combination of the first integrator 43and second integrator 45 and then phase-corrected by the firstdifferentiator 42 and second differentiator 44.

[0051] An experiment was conducted to verify the effect of thisembodiment. While giving vibration by means of a vibration tester to aPC equipped with the HDD 1 of the present invention, servo stabilitysigma [pes] was compared between the condition in which the secondintegrator 45 was operated and the condition in which the secondintegrator 45 was not operated. Results are shown in FIG. 8. As shown inthe figure, it was confirmed that the servo stability in the lowfrequency range was higher when the second integrator 45 was operatedthan when it was not operated. It can be seen that when the secondintegrator 45 is operated, increasing the gain produces greatimprovement in the servo stability in the low frequency range.Incidentally, the high stability at 70 Hz in FIG. 8 is attributable to apeak filter.

[0052] Second Embodiment

[0053] In the above embodiment, the first integrator 43 and secondintegrator 45 which differ in gain are provided and the opening andclosing of the first switch and second switch 47 are controlled in syncwith the operation of the second integrator 45. However, the presentinvention is not limited to the configuration in which twointegrators—the first integrator 43 and second integrator 45—are used. Asingle integrator can give similar effect. An example will be describedas a second embodiment with reference to FIG. 9. The basic configurationof the HDD 1 according to the second embodiment is similar to the HDD 1according to the first embodiment. The difference betweenthem—specifically, the main control section 33 of the MPU 23—will bedescribed here. The same components as those of the first embodiment aredenoted by the same reference numerals.

[0054]FIG. 9 is a block diagram showing the configuration of the maincontrol section 33 according to the second embodiment. FIG. 9A shows thestate in which a magnetic head 8 is in the seek mode while FIG. 9B showsthe state in which the magnetic head 8 is in the track follow mode. Themain control section 33 is composed of a proportional controller 51,differentiator 52, integrator 53, and filter 48. In the secondembodiment, the integrator 53 gain is variable. Specifically, if K13denotes the integrator 53 gain when the magnetic head 8 is in the seekmode and K15 denotes the integrator 53 gain the magnetic head 8 is inthe track follow mode, then K13<K15 holds. Also, let K12 denote thedifferentiator 52 gain when the magnetic head 8 is in the seek mode andlet K14 denote the differentiator 52 gain when the magnetic head 8 is inthe track follow mode, then K12<K14 holds.

[0055] In this way, according to the second embodiment, the gains of thedifferentiator 52 and integrator 53 are varied in sync with the seekoperations of the magnetic head 8. Besides, the gains are set low duringthe seek operations of the magnetic head 8 to ensure stability of theseek operations. When the magnetic head 8 completes a seek operation thegains are set high to ensure servo tracking in the low frequency range.Thus, the HDD 1 of the second embodiment gives the same effect as theHDD 1 of the first embodiment.

[0056] As described above, the present invention has the advantage ofimproving servo tracking characteristics in the low frequency rangewithout impairing the stability of seek operations. Thus, it can reducethe wait time for data read/write operations even on high densitymagnetic disks.

What is claimed is:
 1. A disk drive apparatus, comprising: a disk-likemedium for storing data; a head reads data from and writes data to thedisk-like medium; an actuator which moves the head to a designatedlocation on the disk-like medium; and a position control unit whichpositions the head by controlling a drive of the actuator; the positioncontrol unit comprising: a first integrator which generates a firstgain; and a second integrator which generates a second gain that islarger than the first gain.
 2. The disk drive apparatus according toclaim 1, wherein the first integrator and the second integrator areconnected in parallel.
 3. The disk drive apparatus according to claim 1,wherein: the head performs a seek operation for moving to a designatedlocation on the disk-like medium and a follow operation for reading orwriting data staying at the location; the first integrator operatesduring the seek operation, and the second integrator operates during thefollow operation.
 4. The disk drive apparatus according to claim 3,wherein: a switching unit is provided between the first integrator andthe second integrator; the first integrator operates when the switchingunit closes during the seek operation; and the second integrator or bothfirst integrator and second integrator operate when the switching unitopens during the follow operation.
 5. A disk drive apparatus,comprising: a disk-like medium for storing data; a head which performs aseek operation for moving to a designated location on the disk-likemedium and a follow operation for reading or writing data staying at thedesignated location; an actuator which moves the head to the designatedlocation on the disk-like medium; and a position control unit whichpositions the head by controlling an operation of the actuator; whereinthe position control unit comprises: an integrator which generates acorresponding first gain during the seek operation and a second gaindifferent from the first gain during the follow operation.
 6. The diskdrive apparatus according to claim 5, wherein the second gain is largerthan the first gain.
 7. The disk drive apparatus according to claim 5,wherein the integrator comprises a first integrator which generates thefirst gain and a second integrator which generates the second gain. 8.The disk drive apparatus according to claim 5, wherein the integratorswitches from the first gain to the second gain when a change from theseek operation to the follow operation takes place.
 9. A method of headposition control, comprising: controlling the position of a dataread/write head on a storage medium based on servo information, whereinthe position of the head is controlled based on a first gain when thehead is moving over the storage medium, and the position of the head iscontrolled based on a second gain larger than the first gain when thehead stays at a designated location on the storage medium.
 10. The headposition control method according to claim 9, further comprising thestep of setting the first gain to such a value that will ensure thestability of operation while the head moves over the storage mediumuntil it stops at the designated location.
 11. The head position controlmethod according to claim 9, further comprising the step of setting thesecond gain to such a value that will ensure servo tracking againstdisturbances in the frequency range not higher than 300 Hz while thehead stays at the designated location.
 12. A hard disk drive,comprising: a magnetic disk on which servo information is stored; amagnetic head which seeks the magnetic disk and reads or writes datastaying at a designated location; an actuator which moves the magnetichead to the designated location on the magnetic disk; and a headposition control unit which controls the position of the magnetic headbased on the servo information read out by the magnetic head and whichcomprises an integrator; wherein the integrator generates a first gainand a second gain larger than the first gain, the first gain beinggenerated when the magnetic head does not read or write data and thesecond gain being generated when the magnetic head reads or writes data.13. The hard disk drive according to claim 12, wherein the first gain isgenerated when the magnetic head is seeking.
 14. The hard disk driveaccording to claim 12, wherein the integrator is composed of a firstintegrator which generates the first gain and a second integrator whichgenerates the second gain.
 15. The hard disk drive according to claim12, wherein the integrator generates the first gain and second gain,switching between them.